During the last Ice Age, massive chunks of ice plowed deep grooves and furrows into the Atlantic seafloor from South Carolina to southern Florida. Named keel scours, after the V-shaped structures on boats, the features record the passage of massive glacial floods unleashed from Canada, according to a study published Sunday in the journal Nature Geoscience. The far-traveled floodwaters suggest that future ice sheet melting may be more complex than previously thought.
The icebergs probably came from one of the huge glacial lakes that existed in northern North America when the ice sheets were at their peak, between 22,000 and 12,000 years ago. Ice dams walled off these glacial lakes from the ocean.
When the dams collapsed, floods of frigid freshwater spilled into the North Atlantic, carrying an enormous armada of icebergs. All that cold, fresh water sat on top of hotter, salty water, forcing the warm water to sink, scientists think. This shut down the natural ocean currents that keep the Northern Hemisphere warm. The rapid shift triggered a long cold snap.
"This actually has enormous implications for that model and for what triggers climate change," said study co-author Alan Condron, an oceanographer at the University of Massachusetts at Amherst.
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